1. FIELD OF THE INVENTION
The present invention relates to a polyurethane emulsion composition. More particularly, the present invention relates to a homogeneous stable self-emulsifiable cationic polyurethane emulsion composition.
2. DESCRIPTION OF THE PRIOR ART
Various processes have heretofore been developed and proposed for the preparation of polyurethane emulsions. For example, an emulsifier-free, i.e., a so-called self-emulsifiable, polyurethane emulsion is prepared by forming a urethane prepolymer having terminal isocyanate groups from a polyhydroxyl compound and an organic polyisocyanate, wherein said polyisocyanate is used in an amount in excess of the stoichiometric equivalent amount, chain-extending said urethane prepolymer with a chain extender having a tertiary amino group to form a polyurethane composition containing a tertiary amino group, quaternizing said tertiary amino group and mixing the polyurethane composition with water or an aqueous solution of an acid. According to another process, a polyurethane composition is dispersed in water in the presence of an emulsifier to form a polyurethane emulsion.
In general, polyurethane resins have excellent physical and chemical properties. However, since introduction of chemical cross-linkages is difficult or the emulsifier often remains in the polyurethane resin, the physical and chemical properties of a polyurethane resin film prepared from a polyurethane emulsion prepared by the above process are extremely inferior to those of a film made of a cross-linked polyurethane resin, and therefore, the fields of use of such polyurethane emulsions are greatly restricted.
Polymers having strong cross-linkages are infusible and insoluble, so that the handling of same in the preparation process is generally difficult, and is impossible in many cases. Accordingly, it is substantially impossible to form emulsions by dispersing these polymers into water. In the case of polyurethanes, even if they can be dispersed in water, the resulting emulsions are very unstable in many cases.